FIG 1.

Heteroresistance phenotype toward trimethoprim-sulfamethoxazole in Staphylococcus aureus. (a) Discrepancies between Vitek 2 and disk diffusion in susceptibility testing for trimethoprim-sulfamethoxazole (SXT). Disk diffusion was performed using three different media, Mueller-Hinton agar from Becton, Dickinson (MH_BD), Mueller-Hinton agar from bioMérieux (MH_BM), and Mueller-Hinton agar with 5% horse blood (MHF). SXT-S, SXT susceptible; SXT-R, SXT resistant. (b) Disk diffusion of phenotypically SXT-heteroresistant S. aureus KE7160 on various Mueller-Hinton agars. (c) Low-density heteroresistance phenotype (left panel) and high-density heteroresistance phenotype (right panel) in Kirby-Bauer disk diffusion and MIC test strip.